A portable computer system, such as a personal digital assistant (PDA) or palmtop, is a computer that is small enough to be held in the hand of a user and is thus “palm-sized.” By virtue of their size, portable computer systems are lightweight and so are exceptionally portable and convenient. Portable computer systems are generally powered using either rechargeable or disposable batteries. Because of the desire to reduce the size and weight of the portable computer system to the extent practical, smaller batteries are used. Thus, power conservation in portable computer systems is an important consideration in order to reduce the frequency at which the batteries either need to be recharged or replaced. Consequently, the portable computer system is placed into a low power mode (e.g., a sleep mode or deep sleep mode) when it is not actively performing a particular function or operation.
Some portable computer systems are equipped with radio transmitters and receivers (transceivers) that provide the capability for two-way communication between the portable computer system and a wireless communications network. Accordingly, in addition to the main processor, the portable computer system may include a digital signal processor (DSP) for processing data to be transmitted or data that are received via the transceiver. In the past, when communication occurred between the portable computer system and the wireless network, the portable computer system knew when to expect a transmission. For example, when information or data were being wirelessly transmitted to the portable computer system, it was usually in response to a request initiated by the portable computer system. Thus, the portable computer system was deliberately placed in a receiving mode when a transmission was anticipated, and usually was not in a receiving mode otherwise.
The sophistication of portable computer systems has increased, and therefore portable computer systems are frequently used in applications in which they need to be ready to receive transmitted information at any time, similar to the way a cellular telephone operates. For example, when a cellular telephone is powered on, it is ready to receive an incoming call at any time. Similarly, a portable computer system is ready to receive information at any time that the transceiver is powered on, even if other parts of the portable computer system are in a sleep (low power) mode. Generally, devices transmitting information to the portable computer system have the expectation that the portable computer system will be in a mode in which it can receive the information.
Accordingly, it is desirable for the portable computer system (with a wireless transceiver) to remain “in coverage” when the transceiver is on; that is, it should have a persistent wireless connection to the network. However, due to its portability, there may be occasions in which the portable computer system is moved “out of coverage.” For instance, while in one location, the portable computer system may have established a wireless connection over a particular broadcast channel used by the network. After moving to a different location, a signal over that channel may be too weak, and consequently the connection over that channel may be lost.
Currently, when the transceiver is on and the portable computer system moves out of coverage, the portable computer system will attempt to re-establish a wireless connection to the network over a different channel. Often, as described above, the portable computer system may be in a low power mode. Consequently, in order to re-establish connection with the network, the main processor needs to awaken from the low power mode. The main processor then implements a routine to scan for available channels, to select a channel, and to establish a connection over the selected channel.
However, waking up the main processor is problematic because it can consume a significant amount of power, which is inconsistent with the desire to reduce power consumption and conserve the life of the battery. Accordingly, what is needed is a method and/or system that can be used for re-establishing a wireless connection when an existing connection is lost and that can reduce the amount of power needed to do so. The present invention provides a novel solution to these needs.